Strain weakening of metallic materials

ABSTRACT

A method for controlling the work hardening of a metal component during cold forming by using an electric current passing through the component is provided. The method can include providing a cold forming machine with at least a pair of dies, the machine operable to perform a cold forming operation and apply an electric direct current to a metal component placed in contact with the dies. In addition, the method includes providing a metal component and placing the metal component between the at least a pair of dies. Thereafter, cold forming of the metal component is performed with an electric direct current applied to the component during at least part of the time the component is being cold formed. In some instances, the cold forming is compressive cold forming. The direct current can be applied before or after the cold forming has started and/or be terminated before or after the cold forming has stopped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent Application Ser. No. 60/916,957 filed May 9, 2007, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is related to the deformation of metallic materials, and more particularly, related to the deformation of metallic materials while passing an electric current therethrough.

BACKGROUND OF THE INVENTION

During forming of metals using various bulk deformation processes, the magnitude of force required to perform deformation is a significant factor in terms of the manufacturing of parts. Generally, as the force necessary to deform a given material increases, larger equipment must be utilized, stronger tools and dies are required, tool and die wear increase, and more energy is consumed in the process. All of these factors increase the manufacturing cost of a given component. Therefore, any method or apparatus that would decrease the force required for deformation and/or increase the amount of deformation that can be achieved without fracture would have a significant impact on many manufacturing processes.

Presently, deformation forces are reduced and elongation is increased by working metals at elevated temperatures. However, significant drawbacks to deforming materials at elevated temperatures exist, such as increased tool and die adhesion, decreased die strength, decreased lubricant effectiveness, consumption of materials for heating (which raises energy cost) and the need for additional equipment to be purchased.

One possible method of deforming metallic materials without using such elevated temperatures is to apply an electric current to the workpiece during deformation. In 1969, Troitskii found that electric current pulses reduce the flow stress in metal (Troitskii, O. A., 1969, zhurnal eksperimental'noi teoreticheskoi Kiziki/akademi'i'a nauk sssr—pis'ma v zhurnal .eksperimental' i teoretiheskoi fiziki, 10, pp. 18). In addition, work by Xu et al. has shown that continuous current flow can increase the recrystallization rate and grain size in certain materials (Xu, Z. S., Z. H. Lai, Y. X. Chen, 1988, “Effect of Electric Current on the Recrystallization Behavior of Cold Worked Alpha-Ti”, Scripta Metallurgica, 22, pp. 187-190). Similarly, works by Chen et al. have linked electrical flow to the formation and growth of intermetallic compounds (Chen, S. W., C. M. Chen, W. C. Liu, Journal Electron Materials, 27, 1998, pp. 1193; Chen, S. W., C. M. Chen, W. C. Liu, Journal Electron Materials, 28, 1999, pp. 902).

Using pulses of electrical current instead of continuous flow, Conrad reported in several publications that very short-duration high-density electrical pulses affect the plasticity and phase transformations of metals and ceramics (Conrad, H., 2000, “Electroplasticity in Metals and Ceramics”, Mat, Sci. & Engr., A287, pp. 276-287; Conrad, H., 2000, “Effects of Electric Current on Solid State Phase Transformations in Metals”, Mat. Sci. & Engr. A287, pp. 227-237; Conrad, H., 2002, “Thermally Activated Plastic Flow of Metals and Ceramics with an Electric Field or Current”, Mat. Sci. & Engr. A322, pp. 100-107). More recently, Andrawes et al. has shown that high levels of DC current flow can significantly alter the stress-strain behavior of 6061 aluminum (Andrawes, J. S., Kronenberger, T. J., Roth, J. T., and Warley, R. L., “Effects of DC current on the mechanical behavior of AlMg1SiCu,” A Taylor & Francis Journal: Materials and Manufacturing Processes, Vol. 22, No. 1, pp. 91-101, 2007). Complementing this work, Heigel et al. reports the effects of DC current flow on 6061 aluminum at a microstructural level and showed that the electrical effects could not be explained by microstructure changes alone (Heigel, J. C., Andrawes, J. S., Roth, J. T., Hoque, M. E., and Ford, R. M., “Viability of electrically treating 6061 T6511 aluminum for use in manufacturing processes,” Trans of N Amer Mfg Research Inst, NAMRI/SME, V33, pp. 145-152).

The effects of DC current on the tensile mechanical properties of a variety of metals have been investigated by Ross et al. and Perkins et al. (Ross, C. D., Irvin, D. B., and Roth, J. T., “Manufacturing aspects relating to the effects of DC current on the tensile properties of metals,” Transaction of the American Society of Mechanical Engineers, Journal of Engineering Materials and Technology, 26 pp., to appear in August, 2007; Perkins, T. A., Kronenberger, T. J., and Roth, J. T., “Metallic forging using electrical flow as an alternative to warm/hot working,” Transactions of the American Society of Mechanical Engineers, Journal of Manufacturing Science and Engineering, vol. 129, issue 1, pp. 84-94, 2007). The work by Perkins et al. investigated the effects of currents on metals undergoing an upsetting process. Both of these previous studies included initial investigations concerning the effect of an applied electron wind on the mechanical behavior of titanium. These publications have provided a strong indication that an electrical current, applied during deformation, may be able to lower the force and energy required to perform bulk deformations, as well as improve the workable range of metallic materials. Recently, work by Ross et al. studied the electrical effects on 6Al-4V titanium during both compression and tension test (Ross, C. D., Kronenberger, T. J., and Roth, J. T., “Effect of DC current on the formability of 6AL-4V titanium,” 2006 American Society of Mechanical Engineers—International Manufacturing Science & Engineering Conference, MSEC 2006-21028, 11 pp., 2006).

Electrical current, sometimes termed “electron wind”, is the flow of electrons through a material. The electron wind meets resistance at the many defects found within materials, such as: cracks, voids, grain boundaries, dislocations, and impurity atoms. This resistance, termed “electrical resistance”, is widely known and extensively measured. The greater the spacing that exists between defects, the less resistance there is to optimal electron motion. Conversely, the less spacing between these defects, the greater the electrical resistance of the material.

During loading, material deformation occurs by the movement of dislocations within the material. Dislocations are line defects which can be formed during solidification, plastic deformation or the presence of impurity atoms or grain boundaries. Dislocation motion is the motion of these line defects through the material's lattice structure causing plastic deformation.

Dislocations meet resistance at many of the same places as an electron wind, such as: cracks, voids, grain boundaries, impurity atoms and other dislocations. Under an applied load, dislocations normally move past these resistance areas through one of three mechanisms: cross-slip, bowing or climbing. As dislocation motion is deterred due to localized points of resistance, the material requires more force to continue additional deformation. Therefore, if dislocation motion can be aided through the material, less force is required for subsequent deformation. Theoretically, this will also cause the material's ductility to be subsequently increased.

SUMMARY OF THE INVENTION

A method for controlling the work hardening of a metal component during cold forming by using an electric current passing through the component is provided. The method can include providing a cold forming machine with at least a pair of dies, the machine operable to perform a cold forming operation and apply an electric direct current to a metal component placed in contact with the dies. In addition, the method includes providing a metal component and placing the metal component between the dies. Thereafter, cold forming of the metal component is performed with an electric direct current applied to the component during at least part of the time the component is being cold formed. In some instances, the cold forming is compressive cold forming. The direct current can be applied before or after the cold forming has started and/or be terminated before or after the cold forming has stopped.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic illustration of an apparatus used in an embodiment of the present invention;

FIG. 2 is a graph illustrating the typical strain versus stress for metallic components undergoing strain weakening during compressive deformation when deformed under an applied current;

FIG. 3 is a graph of stress versus current density for 6Al-4V titanium alloy specimens subjected to different strain rates during compression testing wherein an inflection point illustrates where strain weakening begins for the alloy;

FIG. 4 is a graph of stress versus strain for compression testing of 6.35 mm diameter 6Al-4V titanium alloy specimens with each specimen subjected to a different current density during the testing;

FIG. 5 is a graph of stress versus strain for compression testing of 9.525 mm diameter 6Al-4V titanium alloy specimens with each specimen subjected to a different current density during the testing;

FIG. 6 is a graph of stress versus strain for compression testing of 6.35 mm diameter 6Al-4V titanium alloy specimens subjected to a current density of 30 A/mm², the electric current having been initiated at different times for each specimen;

FIG. 7 is a graph of stress versus strain for compression testing of 9.525 mm diameter 6Al-4V titanium alloy specimens subjected to a current density of 23.2 A/mm², the electric current having been initiated at different times for each specimen;

FIG. 8 is a graph of stress versus strain for compression testing of 6.35 mm diameter 6Al-4V titanium alloy specimens subjected to a current density of 35 A/mm², the electric current having been terminated at different times for each specimen;

FIG. 9 is a graph of stress versus strain for compression testing of 9.525 mm diameter 6Al-4V titanium alloy specimens subjected to a current density of 24 A/mm², the electric current having been terminated at different times for each specimen;

FIG. 10 is a graph of stress versus strain for compression testing of a 6.35 mm diameter 6Al-4V titanium alloy specimen subjected to a current density of 35 A/mm², the electric current having been cycled on and off during the test;

FIG. 11 is a graph of stress versus strain for compression testing of two 6.35 mm diameter 6Al-4V titanium alloy specimens subjected to a current density of 35 A/mm² and each specimen compressed with a different strain rate;

FIG. 12 is a graph of stress versus strain for compression testing of a 6.35 mm diameter 6061 T6511 aluminum alloy specimen subjected to a current density of 59.8 A/mm² during compression testing;

FIG. 13 is a graph of stress versus strain for compression testing of 6.35 mm diameter 7075 T6 aluminum alloy specimens with each specimen subjected to a different current density during the testing;

FIG. 14 is a graph or stress versus strain for compression testing of 6.35 mm diameter C11000 copper alloy specimens wit each specimen subjected to a different current density during the testing;

FIG. 15 is a graph of stress versus strain for compression testing of 6.35 mm diameter 464 brass alloy specimens with each specimen subjected to a different current density during the testing;

FIG. 16 is a graph of stress versus strain for compression testing of 6.35 mm diameter A2 steel specimens with each specimen subjected to a different current density during the testing; and

FIG. 17 is a graph of the percentage change in energy required for deformation of an alloy as a function of applied current density to the material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Not being bound by theory, it is proposed and postulated that electron wind provided by an electric current assists dislocation motion by applying a force on the dislocations. This force helps dislocations move easily, thereby requiring less mechanical force to continue their motion. Specifically, this occurs when dislocations meet physical impediments at the different resistance areas and locations.

It is also postulated that, as electrons scatter off different resistant sources, for example the same resistance areas for dislocation motion, the local stress and energy field increases. This occurs since, as electrons strike the areas with a given velocity, there is a decrease in the amount of kinetic energy associated with each electron since the energy is transferred to the resistance area. In turn, this can cause the lattice to locally expand in this area and places or results in these resistance areas being at higher potentials. Therefore, dislocations can move through the areas of resistance with increased local energy fields with less resistance. Since these areas are at a higher potential, less energy is required for a dislocation to move therethrough. In addition, the energy required to break atomic bonds as dislocations move through the lattice structure decreases.

Overall, it is postulated that the effects of current passing through a metallic material should result in a net reduction in the energy required to deform the material while simultaneously increasing the overall workability of the material by substantially enhancing its ductility. Such a postulation is supported by FIG. 17 where the percentage of total energy as a function of applied current density, with respect to a baseline test, is shown. Ideally, the mechanical energy per volume required for deformation is the area under the stress-strain curve. This energy was calculated for the curves of each material using numerical integration. Since some specimens fractured prior to completing the test, the curves were integrated to a strain slightly below the strain where the earliest fracture event occurred for any of the materials tested, 0.2 mm/mm. The other energy accounted for in the system is the electrical energy expended during the deformation. This energy is calculated using the relationship:

${Energy} = \frac{I^{2} \cdot \rho \cdot h \cdot t}{A_{c}}$

where I is current, p is resistivity, h is height, t is test duration and A_(c) is cross-sectional area. The total energy expended to deform the specimen is found by summing the mechanical and electrical energies. As shown, a small addition of electrical energy can greatly reduce the total energy required to deform the part. Moreover, as the density of the electrical energy increases, the total energy needed to deform the part reduces immensely.

The present invention discloses a method for controlling the work hardening of a metal component during cold forming using an electric current passing through the component. As such, the present invention has utility as a manufacturing process. For the purposes of the present invention, the term “work hardening” is defined as the strengthening of a component, specimen, etc., by increasing its dislocation density and such type of strengthening is typically performed by cold forming the component, specimen, etc. In addition, the term “metal” and “metallic” are used interchangeably and deemed equivalent and include materials known as metals, alloys, intermetallics, metal matrix composites and the like.

The method includes providing a cold forming machine, illustratively including a forging apparatus, stamping apparatus, punching apparatus and the like, with the cold forming machine having at least a pair of dies and being operable to perform a cold forming operation. In addition, the machine affords for an electrical direct current to pass through a metal component that has been placed in contact with the cold forming machine dies. After the machine has been provided, a metal component is provided and placed between the dies. Thereafter, cold forming of the metal component is performed while the electrical direct current is passed through the metal component during at least part of the time that the component is being cold formed. In some instances, the cold forming is a compressive cold forming and the electrical direct current is applied to the component before or after the cold forming of the component has been initiated and/or before or after the cold forming has been terminated. It is appreciated that all bulk deformation processes conducted using compression fall within the scope of this method, illustratively including forging, stamping, punching, rolling, extrusion and bending.

Turning to FIG. 1, a schematic representation of an apparatus used with an embodiment of the present invention is shown. An electric current is provided by a direct current (DC) source 100 and deformation to a metal specimen 200 is provided by a compression source 300.

The metal specimen 200 is placed between mounts 310 which are electrically connected to the DC source 100. Upon initiation of the process, the compression source 300 is activated and a compressive force is applied to the specimen 200. While the specimen is under compression, an electrical direct current from the DC source 100 is passed through the mounts 310 and the specimen 200.

Turning to FIG. 2, a schematic representation of the stress as a function of compressive strain for the metallic specimen 200 is shown wherein a decrease in the stress required for continued strain is illustrated and afforded by passing the electric current through the specimen. This phenomena is hereby referred to as strain weakening. In this manner, an apparatus and method for the strain weakening of a material while undergoing compressive deformation is provided.

In order to better illustrate the invention and yet in no way limit its scope, examples of the apparatus and method are provided below.

EXAMPLES Testing Parameters and Setup

A Tinius Olsen Super “L” universal testing machine was used as a cold forming machine and electrical direct current was generated by a Lincoln Electric R35 arc welder with variable voltage output. In addition, a variable resistor was used to control the magnitude of electric current flow. Testing fixtures used to compress metallic specimens were comprised of hardened steel mounts and Haysite reinforced polyester with PVC tubing. The polyester and PVC tubing were used to isolate the testing machine and fixtures from the electric current.

The current for a test was measured using an Omega® HHM592D digital clamp-on ammeter, which was attached to one of the leads from the DC source 100 to one of the testing fixtures 310. The current level was recorded throughout the test. A desktop computer using Tinius Olsen Navigator software was used to measure and control the testing machine. The Navigator software recorded force and position data, which later, in conjunction with MATLAB® software and fixture compliance, allowed the creation of stress-strain plots for the metallic material. The temperature of the specimens was determined during the test utilizing two methods. The first method was the use of a thermocouple and the second method was the use of thermal imaging.

The test specimens consisted of two different sizes. A first size was a 6.35 millimeter (mm) diameter rod with a 9.525 mm length. The second size was a 9.525 mm diameter rod with a 12.7 mm length. The approximate tolerance of the specimen dimensions was ±0.25 mm. After measuring the physical dimensions of a specimen 200 in order to account for inconsistency in manufacturing, the specimen 200 was inserted into the fixtures 310 of the compression device 300 and preloaded to 222 newtons (N) before the testing began. The preload was applied to ensure that the specimen had good contact with the fixtures 310, thereby preventing electrical arcing and assuring accurate compression test results. The tests were performed at a loading rate, also known as a fixture movement rate, of 25.4 mm per minute (mm/min) and the tests were run until the specimen fractured or the load reached the maximum compressive limit of 244.65 kN set for the fixtures, whichever was reached first.

The initial temperature of the specimen 200 was measured using a thermocouple and the welder/variable resistor settings were also recorded. Baseline tests were performed without electric current passing through the specimen using the same fixtures and setup as the tests with electric current. Once the specimens were preloaded to 222 N, and all of the above mentioned measurements obtained, a thermal imaging camera used for thermal imaging was activated and recorded the entire process. During a given test, current and thermocouple temperature measurements were also recorded by hand.

The electricity was not applied to the specimens until the force on the specimen reached 13.34 kN unless otherwise noted. It was found that the amount of strain at which time the electric current was applied affected the specimen's compression behavior and the shape of the respective stress-strain curve. After each of the tests concluded, final temperature measurements were made using the thermocouple. After cooling, the specimen was removed and a final deformation measurement taken.

A precaution was taken to ensure the accuracy of the results by testing the samples for Ohmic behavior. When metals are exposed to high electric currents, they can display non-Ohmic behavior, which can significantly change their material properties. Therefore, tests were conducted with high current densities to ensure that the metallic material tested was still within its Ohmic range. This was accomplished by applying increased current densities to a specimen, and measuring corresponding current and voltage. Using the measured resistivity of the metallic materials, it was verified that the materials behaved Ohmically, that is the Ohm's Law relationship was obeyed.

Testing Results

Initially, tests were conducted in order to find the current density needed to cause strain weakening behavior to occur with 6Al-4V titanium. This density was determined by plotting the decrease in strength for the material with an increase in current density. As shown in FIG. 3, wherein each line represents a constant strain, the stress required to obtain a particular strain as a function of current density was plotted. The graph shows the degree to which strength of the material decreases as the current density increases. In addition, the point where strain weakening begins is the inflection point noted on the graph and shown by the arrow. It is appreciated that this method can be used to estimate the current density at which other metallic materials will exhibit strain weakening.

Turning to FIG. 4, strain weakening exhibited by 6Al-4V titanium is shown. Starting with a current density of approximately 25 amps per square millimeter (A/mm²) and performing tests with higher current densities, a decrease in stress for continued increase in strain was observed at yield points of approximately 0.04 mm/mm strain for 6.35 mm diameter specimens. A comparative test run with no electric current is also shown in the figure for comparison. Thus the unique phenomena of obtaining further deformation of a metallic material with a decrease in stress is shown in this plot, where the baseline material fractured between 0.3 and 0.4 strain, while the specimens deformed under the applied current never fractured. Furthermore, it is seen that the higher the current density, the sooner the material yields and the overall ductility or strain at fracture increases. This decrease in force for continued deformation of the material is well suited for forming parts and components. Similar results are shown in FIG. 5 wherein specimens having a diameter of 9.525 mm were tested.

The effect of initiating the electric current at different times or strains during the compression test is illustrated in FIG. 6 for 6.35 mm diameter specimens and FIG. 7 for 9.525 mm diameter specimens. A current density of 30 A/mm² was used for the 6.35 mm diameter specimens and 23.2 A/mm² for the 9.525 mm diameter specimens. As shown in FIG. 6, specimens where the electric current was initiated at 0.89 kN, 2.22 kN, 13.34 kN and 22.24 kN during the compression testing exhibited behavior that was a function of when the electric current started. For example, the sooner the electric current was applied to the specimen, the lower the yield point of the material. In addition, the sooner the electric current was initiated, the greater the amount of strain weakening exhibited by a particular specimen. The same is true for the 9.525 mm diameter specimens as illustrated in FIG. 7.

It is appreciated that some of these effects can be contributed to temperature, since the sooner the electric current was initiated, the faster and hotter a specimen became. However, it has been established that the effect of an applied current during deformation is greater than can be explained through the corresponding rise in workpiece temperature. It is further appreciated that the amount of work hardening imposed on the specimen can vary as a function of the time load when the electric current is initiated.

The effect of removing the electric current during the testing process was also evaluated. Turning to FIG. 8, a plot of 6.35 mm diameter specimens compression tested with no electricity and with electricity applied during the entire test is shown for comparison. In addition, the two plots wherein the electric current was terminated at a total deformation of 2.032 mm and 3.048 mm are shown. For the 9.525 mm diameter specimens, the electric current was terminated at a total strain of 3.048 mm and 4.064 mm (see FIG. 9). These figures illustrate that the sooner the electric current is terminated the sooner the specimens stop exhibiting strain weakening behavior. In addition, when the electric current is terminated the slope of the stress versus strain curve is steeper than if the electric current is applied to a specimen for the entire test. Furthermore, when the electricity was discontinued early in the test, the material once again was found to fracture.

It is appreciated that the effects of initiating and/or terminating the electric current at different points along a compression/deformation process can be used to enhance the microstructure and/or properties of materials, components, articles, etc. subjected to deformation processes. For example, in some instances, a certain amount of work hardening within a metal component would be desirable before the onset of the strain weakening were to be imposed. In such instances, FIGS. 6 and 7 illustrate that work hardening could be imposed on a component by initiating the electric current through the work piece after plastic deformation has begun. In other instances, a certain amount of work hardening imposed on a work piece after or towards the end of the deformation process could be desirable. As such, FIGS. 8 and 9 illustrate how the termination of the electric current passing through the component at different times or strains of the deformation process result in different amounts of work hardening in the sample. In this manner, physical and/or mechanical properties, illustratively including strength, percentage of cold work, hardness, ductility, rate of recrystallization and the like, of a formed component can be manipulated.

Turning now to FIG. 10, the effect of the electric current on the enhanced forgeability of 6AL-4V titanium was demonstrated by passing a current density of 35 A/mm² through the sample and cycling the current during the test. The electricity was initiated at a force of 13.34 kN and then cycled on and off approximately every 1 mm of deformation up to a total of 4 mm, at which point the electricity remained off until the test was completed. As indicated in the figure, it is visible that the electric current was terminated at approximately 0.225 mm/mm and then reapplied at 0.290 mm/mm. In addition, it is apparent that when the electric current was terminated, the sample exhibited work hardening stress-strain behavior evidenced by an increase in stress for continued plastic deformation. As such, cycling the electric current during compression forming can also afford for the control and manipulation of a components physical and/or mechanical properties.

The effect of varying the strain rate during compression testing is shown in FIG. 11, with a 6.35 mm diameter specimen tested at platen speeds of 12.7 and 83.3 mm/min. The electric current was applied to the specimens at a load of 4.45 kN and remained on during the entire test. As illustrated in FIG. 11, the approximate amount of time the sample exhibits strain weakening is equivalent for both strain rates, however the initiation of strain weakening occurred sooner for the lower strain rate while the end of strain weakening behavior occurred later for the higher strain rate. As such, the amount of work hardening produced in a component before strain weakening occurs can be further manipulated by the strain rate.

Strain weakening behavior via electric current has been demonstrated by other alloys as illustrated in FIGS. 12-16. For example, FIG. 12 shows a stress-strain curve wherein a 6061 T6511 aluminum specimen underwent compression testing with a current density of 59.8 A/mm² applied thereto. As shown in this figure, at a strain of approximately 0.10 mm/mm a decrease in stress was required for additional deformation to occur. Likewise, FIGS. 13-15 illustrate similar strain weakening behavior for 7075 T6 aluminum with a 90.1 A/mm² current density applied thereto, C11000 copper (92.4 A/mm²) and 464 brass (85.7 A/mm²).

The inducement of strain weakening using the current method of the present invention can also be applied to ferrous alloys. FIG. 16 illustrates an A2 tool steel which has been subjected to a number of different current densities while undergoing compression testing. As shown in this figure, at a current density of 45.1 A/mm², the A2 tool steel exhibited a decrease in stress required for an increase in strain after a yield point at approximately 0.02 mm/mm. Thus it is apparent that the method wherein electric current is used to induce strain weakening and control/manipulate physical and/or mechanical properties can be applied to a variety of metallic materials.

The foregoing drawings, discussion and description are illustrative of specific embodiments of the present invention, but they are not meant to be limitations upon the practice thereof. Numerous modifications and variations of the invention will be readily apparent to those of skill in the art in view of the teaching presented herein. It is the following claims, including all equivalents, which define the scope of the invention. 

1. A method for controlling the work hardening of a metal component during cold forming using an electrical direct current passing through the component, the method comprising: providing a cold forming machine, the cold forming machine having at least a pair of dies and operable to perform a cold forming operation to a metal component placed in contact with the dies; providing an electric current source operable to pass electrical direct current through a metal component; providing a metal component; placing the metal component between the at least a pair of dies; cold forming the metal component when it is between the at least a pair of dies; and applying the electrical direct current to the metal component during at least part of the time the metal component is being cold formed, for the purpose of controlling the work hardening of the metal component during the cold forming.
 2. The method of claim 1, wherein the cold forming is a compressive cold forming.
 3. The method of claim 1, wherein the current is applied after the cold forming has started.
 4. The method of claim 1, wherein the current is terminated before the cold forming has been terminated.
 5. The method of claim 1, wherein the current is cycled during the cold forming.
 6. The method of claim 1, wherein a current density of the current is increased during the cold forming.
 7. The method of claim 1, wherein a current density of the current is decreased during the cold forming.
 8. The method of claim 1, wherein the metal is selected from a group consisting of iron, aluminum, titanium, copper and alloys thereof.
 9. The method of claim 1, further comprising the cold forming machine having at least a pair of electrodes for applying the current to the metal component, the at least a pair of electrodes being insulated from the cold forming machine.
 10. A method for controlling the work hardening of a metal component during compressive cold forming using an electrical direct current passing through the component, the method comprising: providing a compressive cold forming machine, the cold forming machine having at least a pair of dies operable to perform a cold forming operation and at least a pair of electrodes operable to apply an electrical direct current to a metal component placed between the dies, the at least a pair of electrodes being insulated from the cold forming machine; providing a metal component; placing the metal component between the at least a pair of dies; compressive cold forming the metal component when it is between the at least a pair of dies; and applying the electrical direct current to the metal component during at least part of the time it is being cold formed, for the purpose of controlling the work hardening of the metal component during the cold forming.
 11. The method of claim 10, wherein the compressive cold forming machine is selected from the group consisting of a forging machine, a stamping machine, a punching machine, a rolling machine, an extrusion machine and a bending machine.
 12. The method of claim 10, wherein the current is applied after the cold forming has started.
 13. The method of claim 10, wherein the current is terminated before the cold forming has stopped.
 14. The method of claim 10, wherein the current is cycled during the cold forming.
 15. The method of claim 10, wherein a current density of the current is increased during the cold forming.
 16. The method of claim 10, wherein a current density of the current is decreased during the cold forming. 